Method and system for providing temporary formation sealant

ABSTRACT

A method and system for providing a temporary sealant within a wellbore of a subterranean formation is disclosed. According to one embodiment, the temporary sealant comprises a particulate material and a liquid. The particulate material and the liquid are mixed to a predetermined dilution ratio. The temporary sealant is pumped into fractures via an open hole of the wellbore. The particulate material accumulates and is left within the fractures to set. Over a predetermined period of time, the particulate material degrades, disintegrates, or dissolves within the fractures.

The present application claims the benefit of and priority to U.S. Provisional Patent Application Ser. No. 61/535,820,408 filed on Sep. 16, 2011, which is hereby incorporated by reference.

FIELD

The present application relates to an enhanced geothermal system (EGS) and to certain situations obtained in oil and gas fields. More particularly, the present invention is a system and method for providing temporary formation sealant,

BACKGROUND

In drilling wells for geothermal, oil and gas, and other energy applications, circumstances arise where drilling fluid enters into a fracture or voids in a rock formation due to high porosity and/or permeability. This can result in the unwanted loss of drilling fluid, also referred to as lost circulation. Lost circulation is the loss of drilling fluid into fractures and other openings or voids in the rock formation. These lost, circulation zones, whether induced or naturally occurring, can he potentially productive, especially in geothermal wells. When flowing into a fracture or a void space in a formation, drilling fluid carries materials such as bentonite, drill solids, barite, lost circulation material (LCM), etc. These materials are difficult or impossible to remove completely after the well has been drilled and completed. In addition, the materials that flow into lost circulation zones may modify the properties of the zone that are important for maintaining permeability. The materials remaining in the lost circulation zones impede or modify production of geothermal fluids, it and gas. This results in reduced productivity of the well and the ultimate economic value of the asset

Use of conventional circulation materials in the drilling fluid or materials that are used as a separate treatment to seal off the fluid losses can result in permanent damage even if they treat and seal off the losses.

SUMMARY

A method and system for providing a temporary sealant within a wellbore of a subterranean formation is disclosed. According to one embodiment, the temporary sealant comprises a particulate material and a liquid. The particulate material and the liquid are mixed to a predetermined dilution ratio. The temporary sealant is pumped into fractures via an open hole of the wellbore. The particulate material accumulates and is left within the fractures to set. Over a predetermined period of time, the particulate material degrades, disintegrates, or dissolves within the fractures.

The above and other preferred features, including various novel details of implementation and combination of elements, will now be more particularly described with reference to the accompanying drawings and pointed, out in the claims, it will be understood that the particular methods and apparatuses are shown by way of illustration only and not as limitations. As will be understood by those skilled, in the art, the principles and features explained herein may be employed in various and numerous embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included as part of the present specification, illustrate the presently preferred embodiment of the present invention and together with the general description given above and the detailed description of the preferred embodiment given below serve to explain and teach the principles of the present invention.

FIG. 1 illustrate a schematic view of an open hole fracture in a wellbore, according to one embodiment;

FIG. 2 illustrates a schematic view of an exemplary process for pumping a temporary formation sealant into open hole fractures, according to one embodiment;

FIG. 3 illustrates a schematic view of an exemplary process for circulating a sealant material out of an open hole, according to one embodiment; and

FIG. 4 illustrates an exemplary process for filling fractures with a temporary sealant, according to one embodiment.

It should be noted that the figures are not necessarily drawn to scale and that elements of structures or functions are generally represented by reference numerals for illustrative purposes throughout the figures. It also should be noted that the figures are only intended to facilitate the description of the various embodiments described herein. The figures do not describe every aspect of the teachings described herein and do not limit the scope of the claims.

DETAILED DESCRIPTION

A method and system for providing a temporary sealant within a wellbore of a subterranean formation is disclosed. According to one embodiment, the temporary sealant comprises a particulate material and a liquid. The particulate material and the liquid are mixed to a predetermined dilution ratio. The temporary sealant is pumped into fractures via an open hole of the wellbore. The particulate material accumulates and is left within the fractures to set. Over a predetermined period of time, the particulate material degrades, disintegrates, or dissolves within the fractures.

In the following description, for purposes of clarity and conciseness of the description, not all of the numerous components shown in the schematic are described. The numerous components are shown in the drawings to provide a person of ordinary skill in the art a thorough enabling disclosure of the present invention. The operation of many of the components would be understood to one skilled in the art.

Each of the additional features and teachings disclosed herein can be utilized separately or in conjunction with other features and teachings to provide temporary formation sealant. Representative examples utilizing many of these additional features and teachings, both separately and in combination, are described in further detail with reference to the attached drawings. This detailed description is merely intended to teach a person of skill in the art further details for practicing preferred aspects of the present teachings and is not intended to limit the scope of the claims. Therefore, combinations of features disclosed in the following detailed description may not be necessary to practice the teachings in the broadest sense and are instead taught merely to describe particularly representative examples of the present teachings.

Moreover, the various features of the representative examples and the dependent claims may be combined in ways that are not specifically and explicitly enumerated in order to provide additional useful embodiments of the present teachings. In addition, it is expressly noted that all features disclosed in the description and/or the claims are intended to be disclosed separately and independently from each other for the purpose of original disclosure, as well as for the purpose of restricting the claimed subject matter independent of the compositions of the features in the embodiments and/or the claims. It is also expressly noted that all value ranges or indications of groups of entities disclose every possible intermediate value or intermediate entity for the purpose of original disclosure, as well as for the purpose of restricting the claimed subject matter. It is also expressly noted that the dimensions and the shapes of the components shown in the figures are designed to help understand how the present teachings are practiced but are not intended, to limit the dimensions and the shapes shown in the examples.

To overcome the problems associated with a lost circulation zone, a temporary formation sealant system (TFSS) is provided. The TFSS treats the lost circulation zone to become productive again after the well has been drilled and completed. The TFSS seals off the lost circulation zone in the open hole section of a well. Once sealed, the hole is drilled to a target depth (TD) after the well is completed. The temporary formation sealant degrades, disintegrates, and/or dissolves over time. As the sealant dissolves, the lost circulation zones regain original permeability and flow capability. The lost circulation zone can he used for production or stimulation of the well. The sealant flows from a treated lost circulation zone, therefore the zone is essentially undamaged from the treatment. Compared to an untreated well, the well treated with TFSS remains productive and provides a viable economic asset. If lost circulation zones were not properly sealed, the value of the well could be greatly reduced and/or become totally unproductive.

FIG. 1 illustrate a schematic view of an open hole fracture 110 in a wellbore, according to one embodiment. Wellbore 100 is formed by drilling a hole into a subterranean formation. A metal pipe (casing) 102 is suspended in the open hole 101 of wellbore 100 and secured by a cement section 105 between the casing 102 and the open hole 101. A last casing shoe 103 is disposed at the bottom of last casing 102. It is understood that open hole fracture 110 shown in FIG. 1 represents any void space to be filled with a temporary sealant, for example, multiple fractures or voids, or a porous or permeable zone.

FIG. 2 illustrates a schematic view of an exemplary process for pumping a temporary formation sealant into open hole fractures 110, according to one embodiment. Sealant material 120 is pumped into open bole 101 to fill fractures or voids 110 within open hole 101. Open fractures or voids 110 are temporarily filled with sealant material 120. Unlike conventional lost circulation material, temporary sealant material 120 degrades, disintegrates, and/or dissolves over time allowing the temporarily filled fractures or voids 110 to reopen for production or injection. Degraded, disintegrated, and/or dissolved sealant 120 enters the drilling fluid or the natural subterranean pore fluid and exits the formation via open hole 101 and/or fractures or voids 110, or absorbed into the surrounding subterranean formulation.

FIG. 3 illustrates a schematic view of an exemplary process for circulating a sealant material out of an open hole, according to one embodiment. Sealant material 120 is pumped into fractures or voids 101, accumulates in pore throats and fracture apertures, and eventually prevents fluid movement. The residue of sealant material 120 and/or well fluid are circulated out of hole 101 during the normal drilling or stimulation process. The circulation of the residue of sealant material 120 does not require special treatment or equipment.

Sealant material 120 remains in place as hole 101 is further drilled to a total depth (ID) and/or completed. After a predetermined period of time, sealant material 120 degrades, disintegrates, and/or dissolves, leaving fractures or voids 110 reopen for production or injection as shown in FIG. 1. The temporary sealant material slowly dearades in the fractures or voids 110, eventually dissolving into the fluids in the rock or diffusing into wellbore 100.

According to one embodiment, sealant material 120 is a fine particulate material, small enough to flow into fractures or voids 110. A variety of materials may be used as sealant material 120 whether alone or in combination. For example, boehmite, polypropylene carbonate, nolybisphenyl carbonate, poly lactic acid, polyethylene terephthalate, and various para-aramids including but not limited to Twaron® and Kevlar® may used for sealant material 120. The particulate material is mixed with liquid (e.g., water) or dissolved into a solvent according to a predetermined dilution ratio. The dilution ratio may be determined by operational and/or well conditions, for example, the pumping capacity and/or robustness of the pump used to pump the particulate mixture, size and number, volume, and/or porosity of fractures or voids 110. For example, the particulate material is diluted with a ratio of 3 to 1 or 4 to 1 (fluid to particulate material),

As sealant material 120 is pumped further into fracture or voids 110, sealant material 120 reduces the permeability to the point where the flow into the fractures or voids 110 is significantly impeded. Impedance is measured by the well head and pumping pressures. When the pumping pressure increases to a threshold pressure that depends upon the particulars of the well such as size and number, and/or volume of fractures or voids 110, it is determined that the sealing has been accomplished. The liquid is squeezed out of the particle pack as pressure continues to apply. As a result, particulate sealant material 120 is left packed off in the fractures or voids 120. The particle pack is able to withstand a differential pressure from both within the fracture or voids 110 and wellbore 100. Sealant material 120 remains intact until it degrades, disintegrates, and/or dissolves over time. The period of time for degradation, disintegration and/or dissolution may be affected by temperature, pressure, and/or chemical conditions as well as the material property of sealant material 120.

It is noted that oil and gas well (O&G) hydraulic fracturing is significantly different from EGS hydroshearing stimulation. The first major difference is that O&G hydraulic fracturing typically involves applying enough pressure and stress on the formation rock to cause tensile failure and create new fractures. In EGS hydroshearing stimulation, however, pump pressure is maintained at a shear failure pressure and is carefully controlled and limited to prevent tensile failure. EGS hydroshearing stimulation opens existing fractures and prevents the creation of new fractures. Once the fracture is opened, the formation rock faces can slip with respect to each other. When the fractures close slightly after stimulation pressure is relieved, the irregularities and disparities between the shifted formation rock faces prevents the fractures from complete closure, leaving a path for water flow with increased permeability.

The second major difference between O&G hydraulic fracturing and EGS hydroshearirm stimulation is that sand and chemicals are purposefully pumped into the open fractures in O&G hydraulic fracturing to hold the fractures open and to aid in the stimulation treatment. On the other hand, EGS stimulation does not inject sand or other proppams into the formation nor are chemicals typically added to the fracturing fluid to stimulate the formations.

According to one embodiment, the present temporary formation sealant system (TFSS) provides a number of unique and advantages. Potentially productive formations within a well are temporarily sealed to allow for production after the well has been drilled or completed. Therefore, TFSS makes wells more productive and increases final economic value of wells. TFSS can be used in oil, gas, and geothermal wells without causing permanent damage to the natural structure of the rock formation. Sealant materials used in TFSS do not require special environment/I permitting, monitoring or disposal nor drilling techniques or equipment other than that used in conventional well drilling and mud-mixing. The sealant materials may be designed to persist for a specified period of time allowing more control over the drilling schedule.

The particulate sealant material is used in combination with water or other solvent to seal off of the fracture and/or voids. According, to one embodiment, the particulate sealant material is a combination of organic compounds, inorganic compounds, natural or synthetic minerals, or other materials. The material properties of such combination result in controlled degradation, disintegration or dissolution. By their nature and design, the particulate sealant material used in TSFF leaves behind minimal residue and prevents damage to the fractures or voids that would reduce permeability. The particulate sealant material may be designed and mixed with water or solvent at a concentration such that no products causing health concerns are produced.

FIG. 4 illustrates an exemplary process for filling fractures with a temporary sealant, according to one embodiment. A temporary sealant is pumped into fractures or voids in a wellbore (401). The temporary sealant is allowed to set within the fractures or voids (402). The formulation is stimulated when applicable before the temporary sealant degrades (403), and the open hole is drilled or completed (404). The temporary sealant degrades, disintegrates, or dissolves within the fractures or voids over a time period (405). Once the temporary sealant degrades, disintegrates, or dissolves, the wellbore is further treated for production or stimulation (406).

Embodiments as described herein have significant advantages over previously developed implementations. As will be apparent to one of ordinary skill in the art, other similar apparatus arrangements are possible within the general scope. The embodiments described above are intended to be exemplary rather than limiting, and the bounds should be determined from the claims. 

What is claimed is:
 1. A method comprising: preparing a temporary sealant comprising a particulate material and a liquid according, the particulate material and the liquid being mixed to a predetermined dilution ratio; pumping the temporary sealant into fractures via an open hole of a wellbore in a subterranean formation; allowing the particulate material to accumulate and set within the fractures; and allowing the temporary sealant to degrade, disintegrate, or dissolve within the fractures over a predetermined period of time.
 2. The method of claim 1 further comprising drilling the open hole after the particulate material is set within the fractures.
 3. The method of claim 2, wherein the open hole is drilled to a total depth (TD).
 4. The method of claim 2, wherein the predetermined dilution, ratio is determined according to a drilling schedule.
 5. The method of claim 1, the predetermined dilution ratio is determined according to a pumping capacity of a pump used to pump the temporary sealant.
 6. The method of claim 1, the predetermined dilution ratio is determined according to a size, a number, a volume, and/or porosity of the fractures.
 7. The method of claim 1 further comprising circulating the liquid of the temporary sealant out of the wellbore.
 8. The method of claim 1, wherein the period is affected by a temperature, a pressure, and/or a chemical condition of the fractures.
 9. The method of claim 1, wherein the temporary sealant is used for oil and gas well (O&G) hydraulic fracturing.
 10. The method of claim 1, wherein the temporary sealant is used for hychoshearing stimulation in an enhanced geothermal system (EGS).
 11. The method of claim 10, wherein the temporary sealant is pumped at a pump pressure under a shear failure pressure.
 12. The method of claim 11, wherein the pump pressure is controlled to prevent a tensile failure of the fractures.
 13. The method of claim 1 further comprising allowing formation rock faces of the subterranean formation to slip with respect to each other.
 14. The method of claim 1, wherein the particulate material is Boehmite or Twaron.
 15. The method of claim 1 further comprising measuring a flow impedance pressure while pumping the temporary sealant, and determining to stop pumping when the flow impedance pressure reaches to a threshold pressure. 